REST end point to query for lists of attachments

In other words: implementation of AttachmentResource.doSearch(..) (see as an example among many here with ProviderResource.)

Some basic query parameters will need to be supported such as:

• patient
• visit
• encounter

This task will encompass adapting the current UI side code to leverage the new REST endpoint rather than ObsResource. See here in the gallery directive.

Important: please study what the kind of requests made by the gallery directive to ensure that AttachmentResource.doSearch(..) will be backward compatible.